B. pertussis expresses a number of proteins including the 69K OMP (pertactin), filamentous hemagglutinin, and pertussis toxin that may promote adherence of B. pertussis to mammalian cells. In order to study the potential role of these proteins in bacterial adherence mutants specifically lacking pertactin, FHA or pertussis toxin are being constructed using the pertussis suicide vector pRTP1. Through the use of antibiotic resistance markers and double recombination events mutants deficient in the expression of pertactin, FHA or both proteins have been constructed and characterized. A decrease in adherence to mammalian cell lines is seen with all the mutants, while the mutant lacking both proteins demonstrates a synergistic effect. Mutants lacking pertussis toxin or all virulent associated proteins are presently being constructed in order to assess the contribution of other bacterial proteins to adhesion.